Developments in recombinant DNA technology and peptide synthesis have made possible the creation of a new generation of drugs. However, small peptides and other agents do not always invoke the immune response necessary for a therapeutic effect. Substances which increase cell-mediated and/or humoral response may be required in the formulation for efficacy. The potency of a variety of agents, particularly antiinfective and antitumor drugs, may be enhanced by stimulation of an immune response.
The cell-mediated immune response ("local immune response") is produced by T-cells or thymus derived lymphocytes. T-cells are able to detect the presence of invading pathogens through a recognition system referred to as the T-cell antigen receptor. Upon detection of an antigen, T-cells direct the release of multiple T-cell lymphokines including the interleukin-2 family (IL-2). IL-2 is a T-cell growth factor which promotes the production of many more T-cells sensitive to the particular antigen. This production constitutes a clone of T-cells. The sensitized T-cells attach to cells containing the antigen. T-cells carry out a variety of regulatory and defense functions and play a central role in immunologic responses. When stimulated to produce a cell-mediated immune response, some T-cells respond by acting as killer cells, killing the host's own cells when these have become infected with virus and possibly when they become cancerous and therefore foreign. Some T-cells respond by stimulating B cells while other T-cells respond by suppressing immune responses.
The antibody or humoral immune response ("systemic immune response") depends on the ability of B-cells, or bone marrow-derived lymphocytes, to recognize specific antigens. The mechanism by which B-cells recognize antigens and react to them is as follows. Each B cell has receptor sites for specific antigens on its surface. When an antigen attaches to the receptor site of a B-cell, the B-cell is stimulated to divide. The daughter cells become plasma cells which manufacture antibodies complementary to the attached antigen. Each plasma cell produces thousands of antibody molecules per minute which are released into the bloodstream. As the plasma cells die, others are produced, so that, once the body is exposed to a particular antigen, antibodies are produced against that antigen as long as the antigen is present in the body. Many B-cells appear to be regulated by the helper T-cells and suppressor T-cells. Helper T-cells appear to stimulate B-cells to produce antibodies against antigens, while suppressor T-cells inhibit antibody production by either preventing the B-cells from functioning or preventing the helper T-cells from stimulating the B-cells. Some B-cells, however, are T-cell independent and require no stimulation by the T-cells.
Immunopotentiators, such as adjuvants, are substances which are added to therapeutic or prophylactic agents, for example vaccines or antigens used for immunization, to stimulate the immune response. Adjuvants cause an accumulation of mononuclear cells, especially macrophages, at the site of injection. Macrophages involved in this first stage of the immune response take in the protein antigens and break them down into peptide fragments which are then exposed on the cell surface where they form a physical association with class II histocompatibility antigens. The T helper cells recognize only protein fragments associated with class II histocompatibility antigen, and not the free undegraded protein. Nonprotein antigens are similarly processed by macrophages or other antigen-presenting cells. The macrophages release monokines from the interleukin-1 family (IL-1) which stimulate the T helper cells to secrete IL-2. The actions of IL-1 and IL-2 result in the clonal expansion of T helper cells. The clonal expansion of T helper cells is followed by their interaction with B-cells, which in turn secrete antibody.
Administration of an adjuvant resulting in stimulation of IL-1 and other cytokines results in a complex spectrum of biological activities. In addition to being a primary immunostimulatory signal, IL-1 proteins have been linked with prostaglandin production, inflammation and induction of fever. IL-1 proteins have been shown to have multiple effects on cells involved in inflammation and wound healing and are known to stimulate proliferation of fibroblasts and attract cells involved in the inflammatory response.
Adjuvants encompass several broad classes including aluminum salts, surface-active agents, polyanions, bacterial derivatives, vehicles and slow-release materials. At present, most adjuvants have been found to stimulate macrophages at the site of action; however, certain adjuvants have been found to act as T-cell replacers enabling B-cells to respond to antigen in the absence of T-cells. An example of such an adjuvant is endotoxin, a B-cell mitogen.
Polynucleotides and other polyanions have been shown to cause release of cytokines. Also, bacterial DNA species have been reported to be mitogenic for lymphocytes in vitro. Furthermore, deoxyoligonucleotides (30-45 nucleotides in length) have been reported to induce interferons and enhance natural killer (NK) cell activity. Kuramoto et al., 1992 Jpn. J. Cancer Res., 83:1128-1131. Oligonucleotides that displayed NK-stimulating activity contained specific palindromic sequences and tended to be guanosine rich. Immune stimulation has also been reported for antisense oligomers that are complementary to the initiation sequence of HIV rev and to the mink cell focus-forming (MCF) envelope gene initiation region. Krieg et al., 1989 J. Immunol., 143:2448-2451; Branda et al., 1993 Biochemical Pharmacology, 45:2037-2043. The MCF sequence is an endogenous retroviral sequence found in mice. In a study designed to determine whether expression of these endogenous viral sequences suppresses lymphocyte activation (as expressed infectious retroviral sequences can), antisense oligonucleotides and analogs complementary to the MCF env gene AUG region were used to inhibit expression of MCF mRNA. This resulted in increased lymphocyte activation. However, this was believed to be a specific effect resulting from inhibition of the target gene, rather than an effect of oligonucleotides per se. In this case both phosphodiester and phosphorothioate oligonucleotides complementary to this target had the same effect, whereas antisense oligonucleotides to other retroviral targets and phosphorothioate control oligonucleotides had no effect. Krieg et al., 1989 J. Immunol., 143:2448-2451; Branda et al., 1993 Biochemical Pharmacology, 45:2037-2043. Branda et al. showed that an anti-rev phosphorothioate oligonucleotide analog is mitogenic in both mononuclear cells from murine spleens and human peripheral blood mononuclear cells. A concentration-dependent stimulation of immunoglobulin production was also observed in vitro and in vivo. This mitogenic effect was specific for B-cells. These effects on B-cells were believed to be specific to this anti-rev oligomer as oligonucleotides complementary to the gag-pol initiation site and the 3' splice site of endogenous retroviral sequences were known not to be stimulatory (Krieg et al., 1989 J. Immunol., 143:2448-2451) and because another phosphorothioate oligonucleotide analog of similar size, targeted to the human p53 protein, did not exhibit the same effect. The data suggested that endogenous retroviruses may suppress lymphocyte activation and that antisense oligonucleotides specific for these inhibitory retroviruses may reverse this suppression and stimulate B-lymphocytes. Though Branda et al. speculated about the possibility that the immune stimulation associated with this oligomer may be independent of its antisense activity, for example, contamination with endotoxin, no evidence for this could be found. Furthermore, the lymphocyte stimulation seen was to an extent not usually seen with exposure to double-stranded RNAs, which stimulate lymphokines. Immune stimulation was concluded not to be a general property of oligodeoxynucleotides, as they have been used by others to inhibit T-cell function. Branda et al., 1993 Biochemical Pharmacology, 45:2037-2043.
The ability to reverse transforming growth factor-.beta.(TGF-.beta.)-mediated cellular immunosuppression in malignant glioma by addition of TGF-.beta.2-specific phosphorothioate-antisense oligonucleotide analogs (TGF-.beta.2-S-ODN's) has also been reported. Jachimaczak et al., 1993 J. Neurosurg, 78:944-951. TGF-.beta., an immunosuppressive factor produced by malignant gliomas, is characterized by a wide range of immunoregulatory properties including depression of T-cell mediated tumor cytotoxicity, inhibition of IL-1- or IL-2-dependent T-cell proliferation, lymphokine-activated killer and natural killer cell activation, generation of cytotoxic macrophages and B-cell function. The oligonucleotide analogs in these experiments were used to block TGF-.beta. protein synthesis at the translation level. In in vitro studies, preincubation of tumor cell cultures with TGF-.beta.2-S-ODN's enhanced lymphocyte proliferation up to 2.5 fold and autologous tumor cytotoxicity up to 60%. Jachimaczak et al. suggested these observations may have implications for in vivo and in vitro activation of a cellular immune response against autologous malignant glioma cells by inhibiting TGF-.beta. synthesis.
Thus, as illustrated by the above-described studies, antisense oligonucleotides and analogs have been used to specifically inhibit expression of genes implicated in immunosuppression, thus reversing the immunosuppressive effects.
An antisense oligonucleotide targeted to the cellular proto-oncogene c-myb has been demonstrated to block T-cell proliferation in peripheral blood mononuclear cells. Gewirtz et al., 1989 Science, 245:180-183. Antisense oligonucleotides targeted to interleukin-2 (IL-2) have been shown to specifically inhibit T-cell functions, i.e., proliferation in response to allo-antigen or PHA and IL-2 production. Kloc et al., 1991 FASEB J., 5:A973.
Thus, antisense oligonucleotides have been used to specifically inhibit the expression of genes involved in T-cell proliferation, thus blocking proliferation and resulting in an immunosuppressive effect.
Phosphorothioate monomers and congeners thereof also have been demonstrated to affect humoral and cell-mediated immune responses. It was shown that mice treated with O,O,S-trimethyl phosphorothioate (OOS-TMP), a contaminant of malathion and other organophosphate pesticides, developed immunosuppression characterized by a decreased ability to make either humoral or cell-mediated immune responses to subsequent immunizations. Rodgers et al., 1987 Toxicol. Appl. Pharmacol., 88: 270-281. On the contrary, O,S,S-trimethylphosphorodithioate (OSS-TMP) enhanced the generation of humoral and cell-mediated immune responses in mice. Rodgers et al., 1988 Toxicol., 51:241-253.
Bacterial DNA and certain synthetic polynucleotides, both single- and double-stranded, can stimulate proliferation of lymphocytes in mice. One such example is AMPLIGEN.RTM. [polyI:poly(C.sub.12 U), HEM Research Inc., Rockville, Md]., a double-stranded RNA (dsRNA) which acts as a lymphokine to mediate cellular immune activity. This includes killer cell modulation, macrophage modulation, B-lymphocyte modulation, tumor necrosis factor modulation, interferon modulation and modulation of interferon-induced intracellular enzymes. AMPLIGEN.RTM. has been reported to stabilize T4 cell counts in patients with AIDS-related complex and to have antineoplastic effects. AMPLIGEN.RTM. is a specific form of mismatched dsRNA which has a uridine substituted for every twelfth cytosine in the poly(C) strand. Poly(I):poly(C) without this mismatching was highly immunogenic but proved to be severely toxic and was abandoned as a clinical candidate in the 1970s. U.S. Pat. No. 5,194,245.
Certain synthetic oligonucleotides and analogs have been shown to be mitogenic in vitro. These oligonucleotides were polydeoxyguanosine, polydeoxycytosine or a mixture of the two. Phosphorothioates were found to be more active than the corresponding phosphodiesters. Pisetsky et al., 1993 Life Sciences, 54:101-107. Unmethylated CpG dinucleotides, in either bacterial DNA or synthetic deoxyoligonucleotides, have recently been found to induce B-cell activation. Krieg et al., 1995 Nature, 374:546-549. In addition, a 21-mer phosphorothioate oligonucleotide analog, ISIS 1082 (SEQ ID NO: 2), was shown to stimulate proliferation and antibody production by murine B cells. This oligonucleotide is complementary to the translation initiation codon of the herpes simplex virus UL13 gene. It was concluded that the mitogenic effects of this and certain other oligonucleotides on B cells may be due to preferential uptake of phosphorothioates and other mitogenic oligonucleotides by B cells, and that the enhanced penetration promotes a high intracellular concentration of these compounds, leading to non-specific activation.
Oligonucleotides having a sequence identical to a portion of the sense strand of the mRNA encoding the p65 subunit of NF-kB, a DNA binding protein, were found to stimulate splenic cell proliferation both in vitro and in vivo. The proliferating spleen cells were shown to be B cells. Immunoglobulin secretion and NF-kB activity in these cell lines was also increased by the sense oligonucleotide. Both phosphodiester and phosphorothioate sense oligonucleotides stimulated the splenocyte proliferation. The antisense phosphorothioate oligonucleotide complementary to the same region of p65 did not have this effect, and the stimulatory effect was abolished by mixing the sense and antisense oligonucleotides. Sense oligonucleotides having two mismatches from the target sense sequence also failed to elicit the proliferative effect. It was concluded that this was a sequence-specific effect which may involve direct binding of the sense sequence to specific proteins. Mcintyre et al., 1993 Antisense Res. and Devel., 3:309-322.
It has now been found, surprisingly, that oligonucleotide analogs having at least one phosphorothioate bond can induce stimulation of a local immune response. This immunostimulation does not appear to be related to any antisense effect which these oligonucleotide analogs may or may not possess. These oligonucleotide analogs are useful as immunopotentiators, either alone or in combination with other therapeutic modalities, such as drugs, particularly antiinfective and anticancer drugs, and surgical procedures to increase efficacy. In addition, the antiinfective and anticancer effects already possessed by certain antisense oligonucleotide analogs are enhanced through such immune stimulation.
It has also been found that oligonucleotide analogs having at least one phosphorothioate bond can be used to induce stimulation of a systemic or humoral immune response. Thus, these oligonucleotides are also useful as immunopotentiators of an antibody response, either alone or in combination with other therapeutic modalities.